Loved the episode, a few of the typical unrealistic big turn abounds, the main one for me being the bad guys start out like a bunch of SAS soliders killing everyone who moves before they even have a chance to raise their gun but at the end are being picked off by a basically rookie agent.
Overall great, the story was good, the dialogue was excellent, I don't know why people are complaining about the blood thing. He was B negative, (not AB- as listed by another reviewer) it's not really that rare... Someone with B- can also take O- blood.
Random FYI for blood:
You have to match - or +
O's can donate to anyone (universal donor) but can only accept O blood.
AB can receive blood from anyone (universal receiver) but their blood is useless to anyone else except other AB's.